2010 Silverado rip off ~ 17" Spare Tire w/ 18" Wheels

I bought my 2010 Silverado in June and went to get tires rotated as the manual stated and tire shop said they couldn't as the spare was a seventeen inch instead of an eighteen.
Called dealer they said call GM. Called Gm they said it doesn't come with the option of 18'. I asked why? No explanation. She asked if it was stated on my window tag. I said no. But i also told her it didn't say I wasn't getting 18" all the way around.
case was closed and stated they resolved the issue. WHAT?
Has any one else experienced the same issue? And gotten a better resolve?

So, your issue was resolved the same way as the "excessive cab noise from the vent" issues! Yours sounds like a good question for the GM Customer Service Rep. I'd like to see what they say.
My guess is they had several thousand leftover 17" wheels & tires & some wise corporate exec in the middle of scarfing doughnuts & slurping coffee said, hey lets just put them in the spare wells on the new trucks. We'll save millions of dollars cuz we don't have to outfit them with 5 new 18"s, plus we get rid of all these extras. I would bet that there are thousands of these & owners just don't know it because they haven't looked or needed their spare yet.

** Enkeis solution below is good for 4 tire rotation & a lot of owners do this even when all 5 tires match.

I am also showing in my resources that the spare comes standard as 17''. I do not have further information as to reasoning behind this. If you have further questions, please feel free to contact me directly.

Did you really think you would find a matching spare under the bed? And what would the spare have to do we rotating anyways? Would you want to mount and balance 1 tire every time you had your tires rotated?

So the cost of mounting and balancing a tire say 10 times over 60k miles (I rotate every 3k) and paying someone to rotate your tires is cost effictive over just rotating the 4 tires you have yourself???? AND you would then have to go and buy 5 new tires rather than 4. Where is the cost savings? The stock tires on these new trucks are crap and I could see if you had a set of 33" Toyo's or something all mounted on aftermarket wheels.

Alston, Why would you have to mount & balance the spare just because you involved it in the 5 tire rotation pattern? Isn't it suppose to be mounted & balanced from the factory just like the other 4?
If GM isn't balancing the spares, then there's going to be even more pizzed off owners when they put their out of balance spare on & it thumps & shakes the crapola outta them

stephan, the spare steel wheel usually doesn't match the other 4 wheels so I think what Alston means is you would have to unmount and remount the spare with another tire and wheel. Most people rotate just the 4 tires. I hope I explained that right . LOL.